Beamer: frame number in split theme footline

Yet again somebody in the mrunix forum asked for an advice how to put the frame number into the footline of his beamer presentation. He was using the “Warsaw” outer theme. The first solution

\setbeamertemplate{footline}[frame number]

will just overwrite the “Warsaw” footline.

Possible solutions are: to use a different outer theme or to change the “Warsaw” footline. “Warsaw” uses the split outher theme, a workaround for insertion of the frame number should consider that and will be usable for other themes like “Copenhagen”, “Luebeck” and “Malmoe”. Inspection of the file beamerouterthemesplit.sty reveals that the footline uses the \insertshorttitle macro in its right part. So a quick workaround could be to redefine that macro: